The present disclosure generally relates to a method and apparatus for preparing gypsum products from starting materials including calcined gypsum and water, and more particularly to an improved apparatus for use in conjunction with a slurry mixer used in supplying agitated gypsum slurry to a wallboard production line.
It is well known to produce gypsum products by dispersing calcined gypsum in water to form a slurry, then casting the slurry into a desired shaped mold or onto a surface, and allowing the slurry to set to form hardened gypsum by reaction of the calcined gypsum (calcium sulfate hemihydrite or anhydrite) with the water to form hydrated gypsum (calcium sulfate dihydrate). It is also well known to produce a lightweight gypsum product by mixing an aqueous foam into the slurry to produce air bubbles. This will result in a desired distribution of voids in the set gypsum product. The voids lower the density of the final product, which is often referred to as “foamed gypsum.”
Prior apparatus and methods for addressing some of the operational problems associated with the production of foamed gypsum are disclosed in commonly-assigned U.S. Pat. Nos. 5,638,635; 5,643,510; 6,494,609; and 6,874,930; all of which are incorporated by reference. In the present disclosure, a mixer includes, but is not limited to, a pin mixer, multipass mixer, pinless mixer, or other types of mixers commonly used in the formulation of gypsum slurries in the production of gypsum wallboard.
It is known in the art to produce wallboard panels with multi-layer gypsum construction, including a first gypsum layer located adjacent a face paper and having a first density, and a second gypsum layer applied upon the first layer. The second layer has a second density, and the density of the second layer is lower than that of the first layer. The higher density of the first layer, achieved by the injection of less foam or water, has been found to bond more securely to the face paper.
To efficiently deliver these two different density gypsum slurries, two separate extractor ports are used. Thus, a discharge gate of the mixer has a first extractor port configured for generating the higher density slurry for the first gypsum layer, and a second extractor port configured for generating the lower density slurry for the second gypsum layer. Typically, the first extractor port is disposed on a mixer sidewall, and connected to a separate entrance for receiving the mixed slurry. To address the chronic problem of unwanted premature setting of slurry that creates lumps in the mixture, an inlet opening of the discharge gate for receiving the mixed slurry is typically equipped with lump bars or grating. These bars prevent slurry lumps from entering into the discharge gate.
However, in certain applications, the grating is disposed too closely to the first extractor port, and causes slurry flow problems when the mixed slurry is delivered to the first extractor port. Specifically, fibers tend to accumulate, prematurely set and subsequently block the first extractor port, preventing the higher density slurry from entering the first port. As a result, all of the mixed slurry is delivered to the second extractor port only, and no higher density slurry is produced for the first gypsum layer. This results in bonding and strength problems in the multi-layer gypsum construction. Therefore, there is a need for an improved discharge gate having enhanced extractor ports for providing various density slurries during the wallboard production.